Twice I've been caught out with "foreign" climates. Once in New York State on a boiling hot day in July - me and a pal in shorts and t-shirts decided to go visit a wolf sanctuary up in the mountains (guided tour). [censored] freezing with snow on the reserve in the mountains. Luckily the tour guides were used to this happening and loaned us both the most stinkyest, horriblest, ill-fitting jackets they had in "lost property".
The second time was a 2 day trip to the Sahara desert. Typically bakingly hot and desert-like during the day. Come night time the temperature plummeted to below freezing. Guess who wasn't expecting that from a "desert"? Aye, me. We were even told to pack warm clothes for the evening ... so I took a fleece that I'd flown in! Woefully inadequate, even indoors.
Even in this country, camping - sitting in my tent on a night, it's cold and I wear a padded jacket (synthetic as I too don't "do" down for ethical reasons).
So.... If a donkey is carrying your gear to each stopping for the evening point then get an insulated jacket for the evening that can go in your camp pack. That way you've got something warm and dry (not sweat wicked) to sit around in.
On the move, if layers work for you then stick with that.
Anyhow, that's my two-penneth's worth